This research project is concerned with the identification and characterization of autoantibodies in the sera of patients with systemic lupus erythematosus and other systemic rheumatic diseases. The autoantibodies are characterized primarily in terms of their specific reaction with cellular antigens. We have devoted a large proportion of our efforts to the characterization of certain nuclear acidic antigens which are associated with nuclear chromatin and which participate in antigen antibody reactions with the autoantibodies present in the human diseases described above. These nuclear acidic antigens have been identified as the Sm nuclear antigen and nuclear ribonucleoprotein. In addition to the nuclear acidic antigens described above, recent studies have led to the identification of three other cellular antigens which are specific reactants for autoantibodies present in the sera of patients with Sjogren's syndrome and rheumatoid arthritis. BIBLIOGRAPHIC REFRENCES: Inami, Y.H., R.M. Nakamura and E.M. Tan. Microhemagglutination test for the detection of nucleoprotein Ab in systemic lupus erythematosus. Am. J. Clin. Path. 64:65-74, 1975. Alspaugh, M.A. and E.M. Tan. Antibodies to cellular antigens in Sjogren's syndrome. J. Clin. Invest. 55:1067-1073, 1975.